Method for Starting an Engine Automatically

ABSTRACT

A method for improving starting of an engine that may be automatically started is provided. In one example, spark timing of an automatically started engine is in advance of spark timing for an operator requested engine start. The approach may reduce vehicle driveline disturbances.

FIELD

The present description relates to a method for improving starting of anengine. The method may be particularly useful for engines that may beautomatically started in response to engine operating conditions.

BACKGROUND AND SUMMARY

Engines may be automatically stopped and restarted automatically in theabsence of an operator engine start request (e.g., an operator startrequest via a key or pushbutton) to conserve fuel. In one example, theengine may be stopped when predetermined conditions occur. For example,the engine may be stopped during a time when a vehicle brake pedal isdepressed and when there is an absence of a driver requested enginetorque. The engine may be restarted when predetermined conditions occur.For example, the engine may be restarted when the operator releases thebrake pedal. However, if the engine is stopped and then restarted whilea transmission of the vehicle is in a gear, the vehicle operator mayexperience a torque disturbance within the vehicle driveline (e.g.,transmission, driveshaft, and vehicle wheels). The torque disturbancemay be related to an amount of torque transmitted from the engine to thedriveline via a torque converter. In particular, the torque convertermay transmit torque from the engine to the vehicle driveline such thatmore engine torque is transmitted to the vehicle driveline at higherengine speeds.

The inventors herein have recognized the above-mentioned disadvantagesand have developed a method for starting an engine, comprising: crankingthe engine via a starter; and adjusting a spark timing for a cylinder ofthe engine to a timing retarded of top-dead-center compression stroke ofthe cylinder in response to a request to automatically start the engine,the spark timing for a first combustion event in the cylinder since astop of the engine.

By providing spark to a cylinder of an engine at timing retarded oftop-dead-center compression stroke it may be possible to start theengine while a transmission coupled to the engine is in drive such thatthe engine speed runs up to idle speed and driveline torque disturbancesare reduced. In one example, spark timing is retarded such that averageIMEP during a cylinder cycle is less than 4 bar. In this way, enginespeed may be controlled such that the possibility of driveline torquedisturbances may be reduced.

In another aspect of the present disclosure the inventors herein haveprovided a method for starting an engine, comprising: cranking theengine via a starter; in response to a controller requested enginestart, adjusting spark timing of the engine to a first timing; and inresponse to an operator requested engine start, adjusting spark timingof the engine to a second timing, the second timing different than thefirst timing.

By providing different spark timings for controller initiated enginestarts (e.g., engine starts in response to selected controller enginerestart conditions being met and without an operator request to startthe engine) and operator initiated engine starts (e.g., an enginerestart responsive to an operator's request to restart an engine via akey-on or pushbutton input), it may be possible to limit an amount ofengine torque transmitted to a vehicle driveline and provide enoughtorque to robustly start the engine.

For example, during a controller initiated engine start when the engineis warm, it may be desirable to provide spark at timing well in advanceof MBT spark timing (e.g., minimum spark advance for best engine torque)so that less engine torque is provided by the engine as compared to whenspark is provided to the engine at MBT spark timing. In this way, enginetorque can be limited to control the amount of torque delivered to thevehicle driveline even when engine cylinders are full of air after anengine stop. On the other hand, it may be desirable to provide spark tothe engine at a second timing when the engine is warm in response to anoperator requested start when a transmission is in park.

In one example, spark provided to the engine may be retarded when anoperator requests an engine start as compared to when a controllerinitiates an engine start. The spark timing during the operatorinitiated engine start may provide additional engine torque so that theengine accelerates at a higher rate and provides a stronger indicationto the driver that the engine is started. In still other examples,higher torque may be provided during an operator initiated engine coldstart to overcome engine friction at lower engine temperatures. Thus, itmay be desirable to provide different spark timings to an enginedepending on whether or not the engine start is requested by anoperator.

The present description may provide several advantages. In particular,the approach may improve engine starting consistency. Further, theapproach may provide improved engine emissions when a controllerinitiates an engine restart. For example, the engine may be restartedsuch that lower pressure combustion occurs during a controller initiatedengine restart since lower pressure spark timing is adjusted away fromMBT spark timing. Consequently, less NOx may be formed in enginecylinders during a controller initiated engine restart. Further, theapproach may improve a driver's perception of vehicle starting when theengine is started automatically by reducing driveline torquedisturbances.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings, where:

FIG. 1 is a schematic diagram of an engine;

FIGS. 2 and 3 are prophetic plots of signals of interest during anengine starting sequence;

FIG. 4 is an example flowchart for stopping an engine;

FIG. 5 is an example flowchart for starting an engine in response tooperator and controller initiated engine starts; and

FIG. 6 is an example prophetic plot of engine IMEP and spark timing.

DETAILED DESCRIPTION

The present description is related to improving starting of an enginethat may be started via operator or controller initiated startingrequests. In one non-limiting example, the engine may be configured asillustrated in FIG. 1.

Engine spark may be controlled as shown in the sequence illustrated inFIGS. 2 and 3. In particular, spark may be controlled differentlybetween operator and controller initiated engine starts and stops. Inone example during a controller requested engine start, spark timing ofa cylinder can be adjusted to timing after top-dead-center compressionstroke for a first combustion event in a cylinder since engine stop. Inanother example during a controller requested engine start, spark timingof the cylinder can be adjusted to timing before top-dead-centercompression stroke and before a spark timing of an operator requestedengine start. In this way, engine torque may be limited during acontroller initiated engine start so that less engine torque may betransferred to the vehicle driveline during an engine start. The methodof FIG. 4 describes one method for stopping an engine of a vehicle thatmay be automatically stopped (e.g., in response to selected idle-stopconditions being met and without an operator request to stop the engine)as illustrated in FIGS. 2-3. The method of FIG. 5 describes a method forrestarting an engine that has been stopped by an operator input or via acontroller.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 and exhaust valve 54. Each intake and exhaustvalve may be operated by an intake cam 51 and an exhaust cam 53.Alternatively, one or more of the intake and exhaust valves may beoperated by an electromechanically controlled valve coil and armatureassembly or other known variable valve actuator. The position of intakecam 51 may be determined by intake cam sensor 55. The position ofexhaust cam 53 may be determined by exhaust cam sensor 57.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Alternatively, fuel may be injected to an intake port, whichis known to those skilled in the art as port injection. Fuel injector 66delivers liquid fuel in proportion to the pulse width of signal FPW fromcontroller 12. Fuel is delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, fuel pump, and fuel rail (not shown).Fuel injector 66 is supplied operating current from driver 68 whichresponds to controller 12. In addition, intake manifold 44 is showncommunicating with optional electronic throttle 62 which adjusts aposition of throttle plate 64 to control air flow from air intake 42 tointake manifold 44. In one example, a high pressure, dual stage, fuelsystem may be used to generate higher fuel pressures.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Catalytic converter 70 can include multiple catalyst bricks, in oneexample. In another example, multiple emission control devices, eachwith multiple bricks, can be used. Catalytic converter 70 can be athree-way type catalyst in one example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing force applied byfoot 132; a measurement of engine manifold pressure (MAP) from pressuresensor 122 coupled to intake manifold 44; an engine position sensor froma Hall effect sensor 118 sensing crankshaft 40 position; a measurementof air mass entering the engine from sensor 120; and a measurement ofthrottle position from sensor 58. Barometric pressure may also be sensed(sensor not shown) for processing by controller 12. In a preferredaspect of the present description, engine position sensor 118 produces apredetermined number of equally spaced pulses every revolution of thecrankshaft from which engine speed (RPM) can be determined.

In some embodiments, the engine may be coupled to an electricmotor/battery system in a hybrid vehicle. The hybrid vehicle may have aparallel configuration, series configuration, or variation orcombinations thereof. Further, in some embodiments, other engineconfigurations may be employed, for example a diesel engine.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom-dead-center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top-dead-center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Finally, during the exhauststroke, the exhaust valve 54 opens to release the combusted air-fuelmixture to exhaust manifold 48 and the piston returns to TDC. Note thatthe above is shown merely as an example, and that intake and exhaustvalve opening and/or closing timings may vary, such as to providepositive or negative valve overlap, late intake valve closing, orvarious other examples.

Referring now to FIGS. 2 and 3, signals of interest during selectedengine starting and stopping conditions are shown. FIG. 2 includes fiveplots of interest during a variety of engine starts and stops, whileFIG. 3 includes three plots. The engine is operating in a four cyclemode with intake and exhaust valves opening and closing according to thefour cycle mode. The signals of FIGS. 2 and 3 may be provided via themethods of FIGS. 4 and 5 executed via instructions of controller 12 ofFIG. 1. Each of vertical markers T₀-T₁₀ represents selected times ofinterest within the sequence illustrated in FIGS. 2 and 3. The plots ofFIGS. 2 and 3 occur at the same time and within the same engine system.Thus, time T₁ of FIG. 2 and time T₁ of FIG. 3 occur at the same time.

It should also be mentioned that throughout the description a time sinceengine stop may be expressed as an amount of time the engine has beenrotating since the engine was last stopped.

The first plot from the top of FIG. 2 shows engine speed during theoperating sequence. Engine speed increases in the direction of the Yaxis arrow and is zero at the X axis. The X axis represents time, andtime increases from the left to the right side of the plot.

The second plot from the top of FIG. 2 shows engine air intake throttleposition during the operating sequence. The throttle opening amountincreases in the direction of the Y axis arrow. Thus, more air can passthrough the throttle when the throttle opening is larger. The throttleopening is substantially closed when the throttle trace is at the Xaxis. The X axis represents time, and time increases from the left tothe right side of the plot.

The third plot from the top of FIG. 2 shows engine spark advance duringthe operating sequence. Horizontal line 202 represents top-dead-centercompression stroke of the cylinder receiving spark. Spark timings abovehorizontal line 202 represents spark timings that are retarded fromtop-dead-center compression stroke of the cylinder receiving spark.Spark timings below horizontal line 202 represent spark timings that areadvanced from top-dead-center compression stroke. MBT spark timing canvary with engine operating conditions (e.g., engine speed, enginetorque). The X axis represents time, and time increases from the left tothe right side of the plot.

The fourth plot from the top of FIG. 2 shows an operator initiatedengine start request. The operator initiated engine start request may bevia a key or a pushbutton, for example. Actions by the operator such aspressing an accelerator pedal or releasing a brake are not to beconstrued as operator initiated engine start requests. Rather, suchconditions may be input conditions for a controller or automatic enginestart request. An operator engine start request is present when thesignal is at a high level. The X axis represents time, and timeincreases from the left to the right side of the plot.

The fifth plot from the top of FIG. 2 shows a controller initiatedengine start request. The controller initiated engine start request maybe present after the engine has been automatically stopped and whenselected conditions have been met, excepting an operator engine startrequest. A controller engine start request is present when the signal isat a high level. The X axis represents time, and time increases from theleft to the right side of the plot.

Referring now to the first plot of FIG. 3, a plot of engine temperatureis shown. Engine temperature increases in the direction of the Y axisarrow. The engine temperature may be a coolant temperature, cylinderhead temperature, or some other temperature of the engine. The X axisrepresents time, and time increases from the left to the right side ofthe plot.

The second plot of FIG. 3 represents a trace of an engine air-fuelratio. Horizontal line 302 represents a stoichiometric air-fuel mixture.The engine is supplied a lean mixture when the air-fuel trace is abovehorizontal line 302. The engine is supplied a rich mixture when theair-fuel trace is below horizontal line 302. The X axis represents time,and time increases from the left to the right side of the plot.

The third plot of FIG. 3 represents an alcohol fuel content of fuelsupplied to the engine for combustion. Alcohol content of fuel suppliedto the engine increases in a direction of the Y axis arrow. Gasolinecontent of the fuel increases toward the X axis. The X axis representstime, and time increases from the left to the right side of the plot.

At time T₀, the engine begins to rotate in response to an operatorrequest to start the engine. The throttle position is shownsubstantially closed; however, the throttle is positioned to allow airflow so that the engine can idle. It should be mentioned that the enginecylinders may fill with air during an engine stop since air may leakpast valves while the engine is stopped. As such, pressure in enginecylinders at the time of start may be atmospheric pressure. Further, theamount of air held in engine cylinders during an engine stop may varydepending on the position of the engine. For example, if a cylinder isstopped in the middle of a compression stroke of the cylinder, thecylinder may hold an amount of air related to half the cylinder volumeat atmospheric pressure.

The engine spark advance (e.g., the spark timing of engine cylinders) attime T₀, in particular spark timing for a first combustion event sinceengine stop, is shown advanced of top-dead-center compression stroke sothat spark is delivered to each engine cylinder individually, during acycle of the cylinder receiving the spark, as the cylinder approachestop-dead-center compression stroke. Thus, combustion is initiated via aspark in the cylinder where the spark is delivered beforetop-dead-center compression stroke. The controller initiated enginestart request remains low indicating that the engine is being startedvia the operator. Engine temperature is also low at time T₀ indictingthat the engine is being cold started. The engine air-fuel ratio is leanso as to reduce the amount of hydrocarbons in engine exhaust emissionsduring the cold engine start.

Further, the alcohol content in fuel injected to the engine is lowduring the cold engine start.

At time T₁, engine speed has achieved idle speed and the throttleposition is increasing indicative of an increasing engine torque requestof the engine. Engine spark is shown retarded of top-dead-centercompression stroke to reduce exhaust gas hydrocarbons and to increaseexhaust heating. Spark timing advances through top-dead-centercompression stroke in response to an increasing engine torque request.The operator engine start request and the controller engine startrequest are low after engine start. Engine temperature starts to slowlyincrease as combustion in engine cylinders heat the engine. The engineair-fuel ratio is adjusted to oscillate around a stoichiometric air-fuelratio. The alcohol content or concentration of alcohol in the fuelinjected to the engine remains at a low level at time T₁.

Between time T₁ and T₂, engine speed and throttle position increase anddecrease in response to an operator provided engine torque request asindicated by a changing throttle position. Shortly after T₁, enginespeed increases as the throttle is opened further. Spark is initiallyadvanced following curve 304, and the spark is retarded towardtop-dead-center compression stroke timing as the throttle closes and theengine torque demand decreases. The spark is retarded so that a torquereserve is maintained by the engine. The torque reserve may be tapped byadvancing spark in response to an unexpected torque demand. For example,spark may be advanced by 5 degrees in response to an increase inalternator load. In this way, engine torque can be quickly increasedwithout having to wait for additional air to enter the engine via theintake manifold.

As engine speed decreases, the vehicle reaches operating conditionswhere the engine may be automatically deactivated. In one example, theengine may be automatically deactivated without an operator requestingan engine stop when the engine torque demand is less than a thresholdlevel, engine temperature is greater than a threshold level, and enginespeed is less than a threshold level. The operator and controller enginestart requests remain low between times T₁ and T₂ since the engine isoperating. In addition, the engine air-fuel ratio oscillates aroundstiochiometric conditions and the alcohol content of fuel supplied tothe engine remains at a low level. In an example where the engine iscoupled to an automatic transmission, the automatic transmission mayremain in drive or a gear while the engine is stopped automatically viaa controller. Transmission clutches may be applied or released while theengine is stopped by controlling oil pressure supplied from an electrictransmission oil pump. In other examples, the transmission may beadjusted to a neutral state and vehicle brakes may be applied when theengine is stopped.

At time T₂, the engine is stopped in response to an automatic enginestop. The engine may be stopped via a controller when selected engineoperating conditions occur as described above. Stopping the engineautomatically can conserve fuel since fuel is not required to keep theengine idling. The engine may remain stopped until conditions changesuch that it is desirable to restart the engine. For example, the enginemay be restarted after the operator releases a vehicle brake pedal. Inone example, spark may be retarded from base spark timing during acontroller initiated engine stop so as to increase a temperature of acatalyst positioned in an exhaust system downstream of the engine.

By increasing the catalyst temperature in response to the controllerinitiated engine stop, the engine may stay off for a longer period oftime so that the engine may not have to be restarted as soon due to adrop in catalyst temperature. In the sequence illustrated in FIGS. 2 and3 the engine remains stopped from time T₂ to time T₃.

At time T₃, the engine is restarted automatically via a controllerengaging a starter and supplying spark and fuel to the engine. Thecontroller engine start request goes from a low state to a high stateindicating to restart the engine. The engine restart may be initiated bythe controller in response to a change in operating conditions such asengine temperature or catalyst temperature decreasing, release of abrake pedal, or an operator torque request. An engine starter is engagedwhen the controller engine start request signal goes high. Further, fuelinjection and spark are delivered to commence combustion within enginecylinders. Spark for a first combustion event in each cylinder isadvanced to timing in advance of top-dead-center compression stroke ofthe respective cylinders as shown via curve 306. It can be seen fromFIG. 2 that the spark timing during a controller initiated automaticstart is in advance of spark timing during an operator initiated enginestart. The spark advance during the controller initiated automaticengine start is advanced so that engine torque may be decreased so as tolimit engine speed. Thus, during a controller initiated start, spark maybe advanced more than during an operator initiated start duringsubstantially the same engine operating conditions. In one example, theengine spark is advanced to timing that corresponds to an indicated meaneffective pressure (IMEP) within the cylinder of less than 4 bar. Thus,the spark is advanced (e.g., advanced beyond MBT timing) to reducecylinder torque so that engine speed can be controlled during enginerun-up (e.g., acceleration from cranking speed to engine idle speed). Inthis way, engine speed can be controlled such that there may be lesspossibility of exceeding the desired engine idle speed, or at leastexceeding the desired engine idle speed by only a threshold amount.Engine speed after time T₃ is shown increasing from crank speed androlling up to idle speed with little overshoot. In some examples, thelocation of peak cylinder pressure (LPP) may be adjusted via advancingspark timing so that LPP is before TDC compression stroke for the firstcylinder to combust an air-fuel mixture since engine stop.

In an alternative example, spark timing for at least the firstcombustion event of one or more engine cylinders (e.g., the firstcylinder to combust an air-fuel mixture since engine stop) during anengine start may be retarded from top-dead-center compression stroke toa timing where IMEP in the cylinder is less than 4 bar for a firstcombustion event of the cylinder as shown via curve 308. Thus, in thisexample, a first combustion event in the engine since engine stop may beinitiated via a spark placed after top-dead-center compression stroke ofthe cylinder receiving the spark. In this way, similar to advancingspark beyond MBT spark timing, spark may be retarded during a firstcombustion event of a cylinder, and during subsequent combustion eventsif desired, such that the cylinder provides less than 4 bar IMEP. Assuch, during a controller initiated start, spark may be retarded morethan during an operator initiated start during substantially the sameengine operating conditions.

The engine is shown starting with a slightly rich air-fuel mixture sothat at least some air that may have entered the catalyst positioneddownstream of the engine in the exhaust system during the engine stopperiod may be used to oxidize hydrocarbons in the rich exhaust mixture.In this way, the catalyst chemistry may be brought back into balance sothat unexpected lean exhaust gas mixtures may be processed efficientlyby the catalyst. In addition, the engine temperature remains relativelywarm and the alcohol content in fuel supplied to the engine remains low.

At time T₄, the throttle opening increases so as to provide additionalair for increasing engine torque. The spark timing is retarded towardtop-dead-center as the engine speed stabilizes near a desired engineidle speed. However, spark timing is advanced at time T₄ in response tochanging engine speed and engine torque. Between time T₄ and time T₅,engine speed increases and then decreases as the position of thethrottle is varied in response to an operator torque demand.

At time T₅, the engine is stopped in response to an operator requestedengine stop. The operator may request an engine stop via a key off.During the operator requested engine stop the spark may be ceased at aspark advance timing that was present immediately prior to the operatorrequested engine stop. Thus, in one example, for an operator requestedengine stop, the spark timing may not be adjusted in response to anoperator requested engine stop.

Between time T₅ and time T₆, the alcohol content of fuel provided to theengine increases. In one example, the alcohol content of fuel suppliedto the engine increases to a level of 85% of the fuel concentration.

At time T₆, the operator engine start request goes to a high level inresponse to an operator requested engine start. In one example, theoperator engine start request signal goes to a high level in response toa key-on by an operator. The engine is cranked and spark and fuel areprovided to the engine in response to the high level operator enginestart request. The spark timing during an operator requested enginestart is retarded as compared to spark timing for a controller initiatedengine start. For example, the spark timing may be retarded closer toMBT spark timing. Thus, the engine may accelerate at a higher rate andto a higher speed during an operator requested engine start as comparedto a controller requested engine start. The spark timing at T₆ isadvanced further than the spark timing at time T₀ in response to enginetemperature and the alcohol content in fuel delivered to the engine. Inparticular, as the alcohol content of the fuel increases the sparktiming is advanced further from MBT spark timing for the firstcombustion event in engine cylinders since engine stop.

Engine speed is shown accelerating the engine above idle speed and thendecaying back to idle speed as time goes on. The engine air-fuel ratiois also shown at stiochimetric conditions. The amount of fuel injectedto the engine may be increased so as to achieve stoichiometriccombustion in the presence of higher alcohol content fuel.

At time T₇, the throttle opening amount is increased in response to anincreasing engine torque demand from the operator. The engine speedincreases as the engine torque amount increases. The engine temperatureremains warm and the engine air-fuel ratio is substantiallystoichiometric during the warm operator requested engine start andduring subsequent engine operation.

At time T₈, the engine is stopped in response to a controller requestedengine stop. Similar to engine operation at time T₂, spark timing may beretarded to a timing later than top-dead-center compression stroke toheat a catalyst within the engine exhaust system. The engine remainsstopped until time T₉ where the engine is restarted. The enginetemperature falls by a small amount between times T₈ and T₉. However,the engine remains warm until the engine restart.

At time T₉, the engine is restarted automatically via a controllerrequested engine start. The controller engine start request signaltransitions from a low level to a high level at time T₉ to initiateautomatic engine starting. The spark timing is shown as set at curve 312to a more advanced timing than the spark timing at T₀, T₃, and T₆. Inthis way, the spark timing for a controller requested engine start isadjusted (e.g., advanced) to control engine speed and in response to thealcohol content (e.g., further advanced) of fuel supplied to the engine.

In an alternative example, the spark timing for the controller requestedengine start for the first combustion event occurring since engine stopmay be adjusted to a timing retarded from top-dead-center compressionstroke as shown by curve 314. Engine speed may be controlled byretarding the spark timing until after top-dead-center compressionstroke of the at least the first cylinder to combust an air-fuel mixtureafter an engine stop. In particular, engine speed may be controlled sothat it does not increase above the desired idle speed by more than apredetermined amount. The retarded spark timing of curve 314 includesretard for IMEP control and increasing alcohol content in the fuel.Thus, curve 314 is retarded further than the spark timings at T₀, T₃,and T₆.

At time T₁₀, the spark timing is shown being retarded from the sparktiming for the first combustion event since engine stop (e.g., theinitial spark timing of curve 314) or advanced from the first combustionevent since engine stop (e.g., the initial spark timing of curve 314).Thus, an engine torque command or a change in operating conditions ofthe engine may cause a transition in spark timing to a spark timingcloser to MBT spark timing. The spark timing may be adjusted in responseto a torque request or throttle input that occurs within a specifiedtime of engine starting. In the example at time T₄, the throttle openingtiming was delayed to allow the spark timing to transition to sparktiming closer to MBT spark timing. The engine speed and engine throttleare shown increasing after time T₁₀ in response to an operator torquerequest.

In this way, spark timing between operator and controller requestedengine starts may be adjusted so as to reduce the possibility oftransferring engine torque to the vehicle driveline even when thetransmission is engaged in a gear. Further, spark timing can be adjusteddifferently between operator requested engine stops and controllerrequested engine stops.

Referring now to FIG. 4, a flowchart for adjusting spark timing duringan engine stop is shown. The method of FIG. 4 is executable viainstructions by controller 12 as depicted in FIG. 1.

At 402, method 400 judges whether or not an engine stop request ispresent. If so, method 400 proceeds to 404. Otherwise, method 400proceeds to exit.

At 404, method 400 judges whether or not the engine stop request is anoperator requested engine stop request. An operator may request anengine stop via a push button or turning a vehicle key to an offposition. If the engine stop request is an operator requested enginestop, method 400 proceeds to 408. Otherwise, method 400 determines thatthe engine stop request is a controller initiated engine stop requestand method 400 proceeds to 406. A controller engine stop request may beprovided when selected operating conditions are met. For example, whenengine speed is less than a threshold speed and when an engine torquedemand is less than a threshold amount.

At 406, method 400 proceeds to retard spark timing for at least onecylinder after the controller initiated engine stop request. In oneexample, the spark timing is retarded to a timing of retarded fromtop-dead-center of compression stroke in the cylinder receiving thespark. Thus, combustion in the cylinder can be delayed so that moreenergy from combusting an air-fuel mixture may be directed to theexhaust system to heat a catalyst in the exhaust system. In this way,the catalyst temperature may be increased prior to engine stop so thatthe engine may not be started as soon in response to a low catalysttemperature. In some examples, spark may be retarded for a predeterminednumber of combustion events since an automatic controller initiatedengine stop.

In some examples, the engine air-fuel mixture may also be richened inresponse to a controller initiated engine stop. By richening the engineair-fuel mixture prior to engine stop, oxygen that enters the catalystduring the engine stop period may be consumed to oxidize hydrocarbons sothat the engine chemistry is more balanced when the engine is restarted.In this way, engine emissions may be reduced during engine starting.

At 408, method 400 stops fuel injection and spark delivered to enginecylinders so that the engine stops. Method 400 proceeds to exit afterstopping spark and fuel flow to the engine.

Referring now to FIG. 5, a flowchart of a method for adjusting spark isshown. The method of FIG. 5 is executable via instructions by controller12 as depicted in FIG. 1.

At 502, method 500 determines engine operating conditions. Engineoperating conditions may include but are not limited to enginetemperature, engine speed, engine torque, controller and operator enginestart and stop requests, and engine position. Method 500 proceeds to 504after engine operating conditions are determined.

At 504, method 500 judges whether or not there is an engine startrequest. If method 500 judges that there is an engine start request,method 500 proceeds to 506. Otherwise, method 500 proceeds to exit.

At 506, method 500 judges whether or not there is a controller enginestart request. A controller engine start request may be initiated via acontroller in response to selected operating conditions. For example, acontroller engine start request may be initiated in response to when anengine has been automatically stopped via the controller and when abrake pedal has been released. If method 500 judges that a controllerinitiated engine start request is present, method 500 proceeds to 508.Otherwise, controller 500 may judge that the engine start request is anoperator requested engine start and method 500 proceeds to 516. Anoperator engine start request may be provided via an operatorspecifically requesting an engine start via a key-on or pushbuttoninput. Lifting of a brake pedal, depressing an accelerator pedal orother similar actions are not construed as an operator engine startrequest.

At 516, method 500 adjusts spark timing to in advance of top-dead-centercompression stroke of the cylinder receiving the spark. For example, aspark may be provided to a cylinder ten crankshaft degrees beforetop-dead-center compression stroke of the cylinder receiving the spark.Thus, spark may be initiated in the cylinder before a piston in thecylinder fully compresses the air-fuel mixture. The spark initiatescombustion in the cylinder so as to accelerate the engine.

At 508, spark timing a first combustion event in a cylinder since enginestop is adjusted. For example, if cylinder number one of a four cylinderengine is a first cylinder to combust an air-fuel mixture since enginestart, spark timing for cylinder number one is adjusted for the firstcombustion event in cylinder number one since engine stop. In otherexamples, spark timing for a first combustion event in each cylinder ofan engine since engine stop is adjusted. For example, spark timing forcylinders one through four of a four cylinder engine are adjusted inresponse to a request to start the engine.

Spark timing for a controller start is adjusted in advance of sparktiming for an operator requested engine start during similar engineoperating conditions (e.g., similar engine temperature and ambient airtemperature) as shown in FIGS. 2-3. For example, if an engine is startedvia an operator request at a warm engine temperature, spark timing maybe adjusted to a timing of ten crankshaft degrees before top-dead-centercompression stroke of the cylinder receiving the spark. On the otherhand, spark timing of a controller requested engine start may be set tofifteen crankshaft degrees before top-dead-center compression stroke sothat engine speed may not rise as high during the controller requestedengine start. By advancing spark further than spark timing during anoperator requested engine start, it may be possible to limit torquetransmitted from the engine to the driveline. Consequently, restartingthe engine while a transmission of the vehicle is in gear may be lessnoticeable to an operator. Further, spark timing may be adjusted inresponse to the concentration of alcohol in fuel injected to the engine.For example, spark timing may be further advanced in response to anincreasing amount of alcohol in fuel injected to the engine when sparktiming is in advance of TDC compression stroke of a cylinder. On theother hand, spark timing may be further retarded in response to anincreasing amount of alcohol in fuel injected to the engine when sparktiming is retarded from TDC compression stroke of the cylinder.

In an alternate example, spark timing for a first combustion event in acylinder since engine stop may be retarded from top-dead-centercompression stroke of the cylinder to limit engine torque during acontroller requested engine start. In yet another example, spark timingfor a first combustion event in each cylinder of an engine since enginestop may be retarded to limit engine torque during a controllerrequested engine start. Method 500 proceeds to 512 after spark timing isadjusted.

At 510, method 500 adjusts the engine air-fuel ratio for the enginestart. The engine air-fuel ratio may be adjusted differently for acontroller requested engine start as compared to an operator requestedengine start. For example, since the transmission may be in gear duringa controller requested engine start, the engine air-fuel ratio may beadjusted richer than an operator requested engine start so as to reduceNOx production during engine starting. Method 500 proceeds to 512 afterthe engine air-fuel ratio is adjusted.

At 512, method 500 judges whether or not to transition spark timing tobase spark timing (e.g., spark timing based on engine speed and load).In one example, spark timing may be transitioned from timing advanced ofbase spark timing to base spark timing in response to a number ofcombustion events since engine stop. In another example, spark timingmay be transitioned from timing advanced of base spark timing to basespark timing in response to a time since engine start. In still anotherexample, spark timing may be transitioned from timing advanced of basespark timing to base spark timing in response to an operator torquerequest. If method 500 judges to transition to base spark timing, method500 proceeds to 514. Otherwise, method 500 returns to 508.

At 508, method 500 adjusts spark timing and cylinder air charge toprovide a desire level of torque at base spark timing. If spark timingis advanced of base spark timing, the engine air amount may be increasedand spark timing may be retarded to control engine torque. If sparktiming is retarded of base spark timing, the engine air amount may beincreased and the spark timing may be advanced to control engine torque.Method 500 exits after spark is transitioned to base spark timing.

Thus, the methods of FIGS. 4 and 5 provide for a method for starting anengine, comprising: cranking the engine via a starter; and adjusting aspark timing for a cylinder of the engine to a timing retarded oftop-dead-center compression stroke of the cylinder in response to arequest to automatically start the engine, the spark timing for a firstcombustion event in the cylinder since a stop of the engine. In thisway, engine torque transmitted through a torque converter during anengine start may be reduced. The method further comprises transitioningfrom spark timing retarded of top-dead-center compression stroke tospark timing at or advanced of MBT spark timing in response to an engineoperating condition. The method includes where the engine operatingcondition is at least one of an operator torque request, an enginespeed, an intake manifold pressure, a number of combustion events sinceengine stop, a temperature, and a time since engine stop. The methodalso includes where transitioning from spark timing retarded oftop-dead-center compression stroke to spark timing at or advanced of MBTspark timing includes transitioning from spark timing retarded oftop-dead-center compression stroke and a first engine torque to sparktiming at or advanced of MBT spark timing and a second engine torque.The method includes where the first engine torque and the second enginetorque are substantially the same engine torque. In one example, themethod includes where the second engine torque is greater than the firstengine torque. The method also includes where the second engine torqueis based on an operator torque request. The method further includeswhere adjusting spark timing of the cylinder includes further retardingspark timing away from MBT spark timing for a first combustion eventsince the stop of the engine as an amount of alcohol in a fuel injectedto the engine increases.

The methods of FIGS. 4-5 also provide for a method for starting anengine, comprising: cranking the engine via a starter; in response to acontroller requested engine start, adjusting spark timing of the engineto a first timing; and in response to an operator requested enginestart, adjusting spark timing of the engine to a second timing, thesecond timing different than the first timing. Thus, in at least oneexample, the method includes controlling spark differently betweencontroller and operator engine starts. The method also includes wherethe first timing is provided during a cylinder cycle of a cylinder ofthe engine, a first combustion event of the cylinder since engine stopoccurring during the cylinder cycle, the first timing advanced of thesecond timing. The method also includes where the first timing isprovided during a cylinder cycle of a cylinder of the engine, a firstcombustion event of the cylinder since engine stop occurring during thecylinder cycle, the first timing after top-dead-center compressionstroke. The method further comprises transitioning the cylinder fromspark timing retarded of top-dead-center compression stroke to sparktiming at or advanced of MBT spark timing in response to an engineoperating condition, the transitioning taking place between a firstcombustion event and a second combustion. The method also includes wheretransitioning to spark timing advanced of MBT spark timing includesretarding spark timing toward MBT spark timing in response to anincreasing torque request during transitioning to spark timing advancedof MBT spark timing. In another example, the method includes where theengine operating condition is a number of combustion events since enginestop or a time since engine stop. The method further includes where fuelis injected at a first timing in response to the controller request tostart the engine and at a second timing in response to the operatorrequested engine start, and where the first timing is different from thesecond timing.

In another example, the methods of FIGS. 4 and 5 provide for starting anengine, comprising: stopping the engine after retarding spark timing inresponse to a request to automatically stop the engine; cranking theengine via a starter; in response to a controller requested enginestart, adjusting spark timing of the engine to a first timing; and inresponse to an operator requested engine start, adjusting spark timingof the engine to a second timing, the second timing different than thefirst timing. The method further comprises adjusting fuel injectiontiming in response to the controller requested engine start, the fuelinjection timing adjusted to provide a rich air-fuel mixture tocylinders of the engine. The method also includes where the fuelinjection timing is further adjusted in response to an alcoholconcentration of a fuel injected to the engine. In one example, themethod includes where the first timing is further adjusted in responseto engine operating conditions. The method further includes where thefirst timing includes providing spark to a cylinder of the engine duringa power stroke of the cylinder, and the method further comprisingtransitioning from providing spark to the cylinder during the powerstroke of the cylinder to a timing advanced of MBT spark timing inresponse to an engine operating condition.

Referring now to FIG. 6, a plot of engine IMEP and spark timing isshown. The Y axis represents IMEP and the X axis represents sparkadvance. A spark advance of zero is indicative of spark timing attop-dead-center compression stroke. A negative spark value is indicativeof spark timing advanced from top-dead-center compression stroke. Apositive spark value is indicative of spark timing retarded fromtop-dead-center compression stroke. Thus, it can be observed from FIG. 6that curve 602 includes two spark timings where 4 bar IMEP may beprovided via engine cylinders. Namely, at 604 and 606 two differentspark timings may provide the same IMEP. At 604, the spark timing isapproximately −28 degrees advanced from top-dead-center compressionstroke. At 606, the spark timing is approximately 30 degrees retardedfrom top-dead-center compression stroke. Thus, IMEP values of less than4 bar can be provided in advance or retarded from top-dead-centercompression stroke. The spark timing at 610 is one example of sparktiming during an operator requested engine start. Thus, the sparktimings of 604 and 606 provide lower IMEP as compared to the sparktiming at 610 so that engine acceleration during a controller requestedengine start may be limited. Note that the spark timing at 604 isadvanced of the spark timing at 610 and that the spark timing at 606 isretarded of the spark timing at 610 and top-dead-center compressionstroke.

As will be appreciated by one of ordinary skill in the art, routinesdescribed in FIGS. 4-5 may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,I3, I4, 15, V6, V8, V10, and V12 engines operating in natural gas,gasoline, diesel, or alternative fuel configurations could use thepresent description to advantage.

1. A method for starting an engine, comprising: cranking the engine viaa starter; and adjusting a spark timing for a cylinder of the engine toa timing retarded of top-dead-center compression stroke of the cylinderin response to a request to automatically start the engine, the sparktiming for a first combustion event in the cylinder since a stop of theengine.
 2. The method of claim 1, further comprising transitioning fromspark timing retarded of top-dead-center compression stroke to sparktiming at or advanced of MBT spark timing in response to an engineoperating condition.
 3. The method of claim 2, where the engineoperating condition is at least one of an operator torque request, anengine speed, an intake manifold pressure, a number of combustion eventssince engine stop, a temperature, and a time since engine stop.
 4. Themethod of claim 2, where transitioning from spark timing retarded oftop-dead-center compression stroke to spark timing at or advanced of MBTspark timing includes transitioning from spark timing retarded oftop-dead-center compression stroke and a first engine torque to sparktiming at or advanced of MBT spark timing and a second engine torque. 5.The method of claim 4, where the first engine torque and the secondengine torque are substantially the same engine torque.
 6. The method ofclaim 4, where the second engine torque is greater than the first enginetorque.
 7. The method of claim 6, where the second engine torque isbased on an operator torque request.
 8. The method of claim 1, whereadjusting spark timing of the cylinder includes retarding spark timingaway from MBT spark timing for a first combustion event since the stopof the engine as an amount of alcohol in a fuel injected to the engineincreases.
 9. A method for starting an engine, comprising: cranking theengine via a starter; in response to a controller requested enginestart, adjusting spark timing of the engine to a first timing; and inresponse to an operator requested engine start, adjusting spark timingof the engine to a second timing, the second timing different than thefirst timing.
 10. The method of claim 9, where the first timing isprovided during a cylinder cycle of a cylinder of the engine, a firstcombustion event of the cylinder since engine stop occurring during thecylinder cycle, the first timing advanced of the second timing.
 11. Themethod of claim 9, where the first timing is provided during a cylindercycle of a cylinder of the engine, a first combustion event of thecylinder since engine stop occurring during the cylinder cycle, thefirst timing after top-dead-center compression stroke.
 12. The method ofclaim 11, further comprising transitioning the cylinder from sparktiming retarded of top-dead-center compression stroke to spark timing ator advanced of MBT spark timing in response to an engine operatingcondition, the transitioning taking place between a first combustionevent and a second combustion.
 13. The method of claim 12, wheretransitioning to spark timing advanced of MBT spark timing includesretarding spark timing toward MBT spark timing in response to anincreasing torque request during transitioning to spark timing advancedof MBT spark timing.
 14. The method of claim 12, where the engineoperating condition is a number of combustion events since engine stopor a time since engine stop.
 15. The method of claim 9, where fuel isinjected at a first timing in response to the controller request tostart the engine and at a second timing in response to the operatorrequested engine start, and where the first timing is different from thesecond timing.
 16. A method for starting an engine, comprising: stoppingthe engine after retarding spark timing in response to a request toautomatically stop the engine; cranking the engine via a starter; inresponse to a controller requested engine start, adjusting spark timingof the engine to a first timing; and in response to an operatorrequested engine start, adjusting spark timing of the engine to a secondtiming, the second timing different than the first timing.
 17. Themethod of claim 16, further comprising adjusting fuel injection timingin response to the controller requested engine start, the fuel injectiontiming adjusted to provide a rich air-fuel mixture to cylinders of theengine.
 18. The method of claim 17, where the fuel injection timing isfurther adjusted in response to an alcohol concentration of a fuelinjected to the engine.
 19. The method of claim 16, where the firsttiming is further adjusted in response to engine operating conditions.20. The method of claim 16, where the first timing includes providingspark to a cylinder of the engine during a power stroke of the cylinder,and the method further comprising transitioning from providing spark tothe cylinder during the power stroke of the cylinder to a timingadvanced of MBT spark timing in response to an engine operatingcondition.